When a semiconductor integrated circuit such as an IC is manufactured, a semiconductor wafer formed of a silicon substrate or the like is generally, repeatedly subjected to various processes such as a film deposition process, an etching process, an oxidation-and-diffusion process, and an annealing process. When a thermal process typified by a film deposition process is performed to a semiconductor, one of important factors is a temperature regulation (management) for a wafer. Namely, in order to increase a film deposition rate of a film to be formed on a wafer surface and/or in order to achieve an interfilm uniformity and an in-plane uniformity with respect to thickness of the film, it is required to regulate (control) a temperature of the wafer with a high precision.
Given herein as an example to describe the temperature regulation is a case where a vertical thermal processing apparatus capable of simultaneously processing a plurality of wafers is used as a thermal processing apparatus. At first, semiconductor wafers supported in a tier-like manner are loaded into a vertical processing vessel, and the wafers are heated by a heating unit disposed on an outer circumference of the processing vessel so that temperatures of the wafers are raised. Then, after the temperatures have been stabilized, a film deposition gas is caused to flow, whereby a film deposition process is performed. In this case, a thermocouple is disposed inside and/or outside the processing vessel, so that a power of the heating unit is controlled based on a temperature obtained from the thermocouple, to maintain the temperatures of the wafers at a predetermined temperature (for example, JP10-25577A and JP2000-77346A).
When the processing vessel has a vertical length enough to receive therein about 50 to 150 wafers, in order to achieve a desired minute (precise) temperature control in the processing vessel, it is preferable to vertically divide the inside space of the processing vessel into a plurality of heating zones and to independently control a temperature of each heating zone. Herein, if a thermocouple is disposed on an experimental dummy wafer itself, a correlation between an actual temperature of the dummy wafer detected by this thermocouple and a temperature detected by another thermocouple disposed inside and/or outside the processing vessel can be previously obtained by an experiment. In this case, by referring to the correlation, there can be realized a proper temperature control for a product wafer when the product wafer is thermally processed.
In addition, in order to measure a temperature distribution of a semiconductor wafer during a thermal process, there has been proposed the following technique (JP2007-171047A). Namely, a plurality of temperature sensors, each having a surface elastic wave (acoustic wave) device, are dispersedly arranged on a surface of a wafer. Radiofrequency signals are transmitted to the respective temperature sensors from a separate antenna that is additionally installed. In response to the radiofrequency signals, the temperature sensors respectively send back second (returned) radiofrequency signals dependent on respective temperatures of the temperature sensors. By receiving and analyzing the (second) radiofrequency signals, a temperature distribution can be obtained (JP2007-171047A).
In the temperature control method for the thermal processing apparatus as disclosed in JP10-25577A and JP2000-77346A, since the thermocouple is not in direct contact with the wafer whose temperature is to be measured, the correlation between an actual temperature of the wafer (product wafer) and a value measured by the thermocouple is not constant at every moment. In particular, there is a possibility that the temperature of the wafer may not be properly controlled when the actual correlation for the product wafer is largely deviated from the previously obtained correlation for the dummy wafer. For example, this deviation may be caused by unnecessary deposits adhering to an inner wall surface of the processing vessel and the like because of repeated film deposition processes, by any change of a gas flow rate and/or a process pressure, and by a voltage variation.
On the other hand, even when a temperature of a wafer is increased and decreased, there is also a demand for controlling the temperature of the wafer. However, it is difficult for the aforementioned method using a thermocouple to meet this demand, because the difference between an actual temperature of the wafer and a value measured by the thermocouple tends to become larger and fluctuate, when the temperature of the wafer is to be increased and decreased.
In order to solve this problem, it can be considered that a thermocouple is disposed on the wafer itself. However, since wires have to be connected to the thermocouple, it is difficult for the thermocouple to follow the wafer when it is rotated and transferred. Further, a metal contamination may be caused by the thermocouple.
As disclosed in JP2004-140167A, in a single-wafer type of processing apparatus, the use of a quartz oscillator can be considered so as to obtain a wafer temperature by receiving an electromagnetic wave dependent on the wafer temperature. However, a heating resistance of quartz is about 300° C. at most. Thus, such measures cannot be applied to a thermal processing apparatus in which a higher temperature process is performed.
Further, in the technique disclosed in JP 2004-140167A, it is necessary to additionally dispose an antenna itself. The antenna has to be disposed in a chamber. Thus, there may be generated a metal contamination for a semiconductor wafer.